source: soft/giet_vm/memo/src/libelfpp/elfpp_access.cc @ 244

/*
    This file is part of Libelfpp.

    Libelfpp is free software: you can redistribute it and/or modify
    it under the terms of the GNU Lesser General Public License as
    published by the Free Software Foundation, either version 3 of the
    License, or (at your option) any later version.

    Libelfpp is distributed in the hope that it will be useful, but
    WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with Libelfpp.  If not, see
    <http://www.gnu.org/licenses/>.

   Copyright (c) Alexandre Becoulet <alexandre.becoulet@free.fr>
*/

#include <stdexcept>
#include <iostream>
#include <cassert>
#include <algorithm>
#include <cstring>

#include <dpp/foreach>

#include <elfpp/access>
#include <elfpp/object>
#include <elfpp/section>
#include <elfpp/symbol>
#include <elfpp/reloc>
#include <elfpp/segment>

namespace elfpp
{

  template <typename bits_t, int width>
  void elfn_access<bits_t, width>::load_symtab(object &obj)
  {
    section &table = obj.get_section(".symtab");

    if (table.get_type() != SHT_SYMTAB)
      throw std::runtime_error("not a symbol table section");

    // get symbol table content
    elf_sym_t *symtab = (elf_sym_t*)table.get_content();
    size_t count = table.get_size() / sizeof (elf_sym_t);

    // get symbol string section
    section &strtab = *table.get_link();
    const char *symstr = (char*)strtab.get_content();

    // create symbol objects from table
    obj.symidx_.resize(count);

    for (unsigned int i = 1; i < count; i++)
      {
        unsigned int idx = swap(symtab[i].st_shndx);

        symbol *sym = new symbol(symstr + swap(symtab[i].st_name));

        obj.symidx_[i] = sym;

        sym->set_value(swap(symtab[i].st_value));
        sym->set_size(swap(symtab[i].st_size));
        sym->set_info(symtab[i].st_info);
        sym->set_other(symtab[i].st_other);

        if (idx > 0 && idx < SHN_LORESERVE)
          {
            section *symsec = obj.secidx_.at(idx);
            if (!symsec)
              continue;

            sym->set_section(*symsec);
            symsec->add_symbol(*sym);

            if (obj.type_ != ET_REL)
              sym->set_value(sym->get_value() - symsec->get_vaddr());

            if (symsec && sym->get_size() > 0 && symsec->get_type() != SHT_NOBITS)
              {
                if (symsec->get_size() < sym->get_value())
                  std::cerr << "elfpp: symbol value above section size " << sym->get_name()
                            << ":" << std::hex << sym->get_value() << std::endl;
                //              else
                //                sym->set_content(symsec->get_content() + sym->get_value());
              }
          }
        else
          {
            sym->set_section_ndx(idx);
            obj.add_symbol(*sym);
          }
      }

    // discard symbol table sections
    delete &table;
    delete &strtab;
  }

  template <typename bits_t, int width>
  void elfn_access<bits_t, width>::load_addend(const object &obj, reloc &r, const elf_rel_t *reltab,
                                               size_t count, int index, uint8_t *data)
  {
    //            r->set_addend(rel_read(obj, type, sec->get_content() + ro));
    uint64_t offset = swap(reltab[index].r_offset);
    r.set_offset(offset);

    switch (obj.machine_)
      {
      case EM_MIPS:
        switch (r.get_type())
          {
          case R_MIPS_26:
            r.set_addend((swap(*(uint32_t*)(data + offset)) & 0x3ffffff) << 2);
            return;

          case R_MIPS_32:
            r.set_addend(swap(*(uint32_t*)(data + offset)));
            return;

          case R_MIPS_HI16: {
            int32_t value = (swap(*(uint32_t*)(data + offset)) & 0xffff) << 16;
            // get next LO16 relocation
            for (index++; index < (int)count && rel_type(swap(reltab[index].r_info)) != R_MIPS_LO16; index++)
              ;
            if (index != (int)count)
              {
                offset = swap(reltab[index].r_offset);
                value += (int16_t)swap(*(uint32_t*)(data + offset));
                r.set_addend(value);
              }
            else
              {
                std::cerr << "elfpp: can not find matching LO16 relocation" << std::endl;
              }
            return;
          }

          case R_MIPS_LO16: {
            int32_t value = (int16_t)swap(*(uint32_t*)(data + offset));
            // get prev HI16 relocation if any
            if (index > 0 && rel_type(swap(reltab[index - 1].r_info)) == R_MIPS_HI16)
              {
                offset = swap(reltab[index - 1].r_offset);
                value += (swap(*(uint32_t*)(data + offset)) & 0xffff) << 16;
              }
            r.set_addend(value);
            return;
          }

          default: ;
          }
        break;

      case EM_ARM:
        switch (r.get_type())
          {
          case R_ARM_PC24:
            r.set_addend(((swap(*(uint32_t*)(data + offset)) & 0xffffff) << 2) + 8);
            return;

          case R_ARM_ABS32:
            r.set_addend(swap(*(uint32_t*)(data + offset)));
            return;

          default: ;
          }
        break;

      default: ;
      }

    std::cerr << "elfpp: unhandled relocation (machine=" << obj.machine_
              << ", type=" << r.get_type() << ")" << std::endl;
    return;
  }

  template <typename bits_t, int width>
  void elfn_access<bits_t, width>::rel_write(const object &obj, enum reloc_e type, void *data, int64_t value)
  {
    uint32_t mask;

    switch (obj.machine_)
      {
      case EM_MIPS:
        switch (type)
          {
          case R_MIPS_26:
            mask = 0x3ffffff;
            if (value & 0x3)
              std::cerr << "elfpp: R_MIPS_26 relocation with 2 LSB set" << std::endl;
            value >>= 2;
            goto done;

          case R_MIPS_32:
            mask = 0xffffffff;
            goto done;

          case R_MIPS_HI16:
            mask = 0xffff;
            value >>= 16;
            goto done;

          case R_MIPS_LO16:
            mask = 0xffff;
            goto done;

          default: ;
          }
        break;

      case EM_ARM:
        switch (type)
          {
          case R_ARM_PC24:
            mask = 0x00ffffff;
            value = (value - 8) >> 2;
            goto done;

          case R_ARM_ABS32:
            mask = 0xffffffff;
            goto done;

          default: ;
          }
        break;

      default: ;
      }

    std::cerr << "elfpp: unhandled relocation (machine=" << obj.machine_ << ", type=" << type << ")" << std::endl;
    return;

  done:
    *(uint32_t*)data = swap(mask & value) | (*(uint32_t*)data & swap(~mask));
  }

  template <typename bits_t, int width>
  void elfn_access<bits_t, width>::load_reltab(object &obj)
  {
    // load all reloaction table sections

    if (obj.type_ != ET_REL)
      return;

    FOREACH2(relsec, obj.get_section_table())
      {
        switch (relsec->get_type())
          {
          case SHT_REL: {
            elf_rel_t *reltab = (elf_rel_t*)relsec->get_content();
            size_t count = relsec->get_size() / sizeof (elf_rel_t);
            obj.rel_with_addend_ = false;

            for (unsigned int i = 0; i < count; i++)
              {
                if (!rel_sym(swap(reltab[i].r_info)))
                  continue;

                reloc *r = new reloc();

                section *sec = relsec->get_info();
                symbol *sym = obj.symidx_.at(rel_sym(swap(reltab[i].r_info)));
                assert(sym);

                r->set_symbol(sym);
                r->set_section(sec);

                reloc_e type = rel_type(swap(reltab[i].r_info));
                r->set_type(type);
                load_addend(obj, *r, reltab, count, i, sec->get_content());
              }

            //          std::cerr << "elfpp: relocation " << i << " offset " << ro << " out of section" << std::endl;

            delete &*relsec;
            break;
          }

          case SHT_RELA: {
            elf_rela_t *reltab = (elf_rela_t*)relsec->get_content();
            size_t count = relsec->get_size() / sizeof (elf_rela_t);
            obj.rel_with_addend_ = true;

            for (unsigned int i = 0; i < count; i++)
              {
                if (!rel_sym(swap(reltab[i].r_info)))
                  continue;

                reloc *r = new reloc();

                section *sec = relsec->get_info();
                symbol *sym = obj.symidx_[rel_sym(swap(reltab[i].r_info))];
                assert(sym);

                r->set_symbol(sym);
                r->set_section(sec);

                r->set_type(rel_type(swap(reltab[i].r_info)));
                uint32_t ro = swap(reltab[i].r_offset);
                r->set_offset(ro);
                r->set_addend(swap(reltab[i].r_addend));
              }

            delete &*relsec;
            break;
          }

          default:
            break;
          }

      }

    obj.generate_symtab_ = true;
  }

  static bool sort_predicate(const symbol *a, const symbol *b)
  {
    return a->get_info() < b->get_info();
  }

  template <typename bits_t, int width>
  void elfn_access<bits_t, width>::save_symtab(object &obj)
  {
    size_t shnum = 1;

    // renumber current section table
    FOREACH(s, obj.get_section_table())
      s->index_ = shnum++;

    // create symbol and associated string sections
    section *symtab = new section(obj, SHT_SYMTAB);
    section *strtab = new section(obj, SHT_STRTAB);
    std::string str(1, '\0');

    symtab->set_name(".symtab");
    symtab->set_entsize(sizeof (elf_sym_t));
    symtab->set_link(strtab);

    strtab->set_name(".strtab");
    strtab->set_flags(SHF_STRINGS);

    obj.add_section(*symtab);
    obj.add_section(*strtab);

    // prepare sorted symbol array

    unsigned int i = 0;
    std::vector<symbol *> table;

    table.resize(obj.get_symbol_table().size());

    FOREACH(sym, obj.get_symbol_table())
      table[i++] = sym->second;

    FOREACH(sec, obj.get_section_table())
      {
        table.resize(i + sec->get_symbol_table().size());

        FOREACH(sym, sec->get_symbol_table())
          table[i++] = sym->second;
      }

    sort(table.begin(), table.end(), sort_predicate);

    for (i = 0; i < table.size(); i++)
      {
        if (ELF_ST_BIND(table[i]->get_info()) != STB_LOCAL)
          break;
      }

    symtab->set_info_last(i + 1);

    // generate symbol table section content

    std::vector<reloc*> reloclist[shnum];
    elf_sym_t symdata[table.size() + 1];
    i = 1;

    std::memset(symdata, 0, sizeof(elf_sym_t));

    FOREACH(sym_, table)
      {
        elf_sym_t &ent = symdata[i];
        symbol *sym = *sym_;

        swap(&ent.st_name, str.size());
        str.append(sym->get_name().c_str(), sym->get_name().size() + 1);
        swap(&ent.st_value, sym->get_value());
        swap(&ent.st_size, sym->get_size());
        ent.st_info = sym->get_info();
        ent.st_other = sym->get_other();

        FOREACH(rel, sym->reloc_tab_)
          reloclist[rel->get_section()->index_].push_back(&*rel);

        if (sym->get_section())
          swap(&ent.st_shndx, sym->get_section()->index_);
        else
          swap(&ent.st_shndx, sym->get_section_ndx());

        sym->index_ = i++;
      }

    strtab->set_size(str.size());
    std::memcpy(strtab->get_content(), str.data(), str.size());

    symtab->set_size(sizeof(symdata));
    std::memcpy(symtab->get_content(), symdata, sizeof(symdata));

    // generate relocation table

    FOREACH(sec, obj.get_section_table())
      {
        if (!sec->index_)
          continue;

        std::vector<reloc*> &rl = reloclist[sec->index_];

        if (rl.empty())
          continue;

        section *reltab = new section(obj, obj.rel_with_addend_ ? SHT_RELA : SHT_REL);

        reltab->set_entsize(sizeof (elf_rel_t));
        reltab->set_link(symtab);
        reltab->set_info(&*sec);

        obj.add_section(*reltab);

        if (obj.rel_with_addend_)
          {
            elf_rela_t reldata[rl.size()];

            reltab->set_name(".rela" + sec->get_name());
            i = 0;

            FOREACH(rel_, rl)
              {
                reloc *rel = *rel_;

                if (symbol *ms = rel->get_mangled_symbol())
                  swap(&reldata[i].r_offset, ms->get_value() + rel->get_offset());
                else
                  swap(&reldata[i].r_offset, rel->get_offset());

                swap(&reldata[i].r_info, rel_info(rel->get_symbol()->index_, rel->get_type()));
                swap(&reldata[i].r_addend, rel->get_addend());
                i++;
              }

            reltab->set_size(sizeof(reldata));
            std::memcpy(reltab->get_content(), reldata, sizeof(reldata));
          }
        else
          {
            elf_rel_t reldata[rl.size()];

            reltab->set_name(".rel" + sec->get_name());
            i = 0;

            FOREACH(rel_, rl)
              {
                reloc *rel = *rel_;

                uint64_t ro = rel->get_offset();
                if (symbol *ms = rel->get_mangled_symbol())
                  {
                    // relocation offset is relative to mangled symbol value
                    if (ro < ms->get_size())
                      rel_write(obj, rel->get_type(), ms->get_content() + ro, rel->get_addend());
                    else
                      std::cerr << "elfpp: relocation offset above mangled symbol size" << std::endl;
                    ro += ms->get_value();
                  }
                else
                  {
                    // relocation offset is relative to mangled section
                    if (ro < sec->get_size())
                      rel_write(obj, rel->get_type(), sec->get_content() + ro, rel->get_addend());
                    else
                      std::cerr << "elfpp: relocation offset above section size" << std::endl;
                  }

                swap(&reldata[i].r_offset, ro);

                swap(&reldata[i].r_info, rel_info(rel->get_symbol()->index_, rel->get_type()));
                i++;
              }

            reltab->set_size(sizeof(reldata));
            std::memcpy(reltab->get_content(), reldata, sizeof(reldata));
          }

      }
  }

  template <typename bits_t, int width>
  void elfn_access<bits_t, width>::read(object &obj, FILE *file)
  {
    // read file header

    elf_hdr_t head_;

    fseek(file, 0, SEEK_SET);
    if (fread(&head_, sizeof (head_), 1, file) != 1)
      throw std::runtime_error("unable to read file");

    obj.word_width_ = (ei_class_e)head_.e_ident[EI_CLASS];
    obj.byteorder_ = byteorder_ = (ei_data_e)head_.e_ident[EI_DATA];
    obj.os_abi_ = (ei_osabi_e)head_.e_ident[EI_OSABI];
    obj.abi_ver_ = head_.e_ident[EI_ABIVERSION];
    obj.type_ = (e_type_e)swap(head_.e_type);
    obj.machine_ = (e_machine_e)swap(head_.e_machine);
    obj.entry_ = swap(head_.e_entry);
    obj.flags_ = swap(head_.e_flags);

    // read segment table
    size_t phnum = swap(head_.e_phnum);
    elf_phdr_t phdr[phnum];

    fseek(file, swap(head_.e_phoff), SEEK_SET);
    if (fread(phdr, sizeof (elf_phdr_t), phnum, file) != phnum)
      throw std::runtime_error("unable to read file");

    // create segment objects

    for (unsigned int i = 0; i < phnum; i++)
      {
        segment *s = new segment(obj);

        s->set_type((p_type_e)swap(phdr[i].p_type));
        s->set_file_offset(swap(phdr[i].p_offset));
        s->set_vaddr(swap(phdr[i].p_vaddr));
        s->set_paddr(swap(phdr[i].p_paddr));
        s->set_mem_size(swap(phdr[i].p_memsz));
        s->set_file_size(swap(phdr[i].p_filesz));
        s->set_flags((p_flags_e)swap(phdr[i].p_flags));
        s->set_align(swap(phdr[i].p_align));

        obj.add_segment(*s);
      }

    // read section table
    size_t shnum = swap(head_.e_shnum);
    elf_shdr_t shdr[shnum];
    obj.secidx_.resize(shnum);

    fseek(file, swap(head_.e_shoff), SEEK_SET);

    if (fread(shdr, sizeof (elf_shdr_t), shnum, file) != shnum)
      throw std::runtime_error("unable to read file");

    // create section objects

    for (unsigned int i = 1; i < shnum; i++)
      {
        sh_type_e type = (sh_type_e)swap(shdr[i].sh_type);

        section *s = new section(obj, type);
        off_t offset = swap(shdr[i].sh_offset);

        obj.secidx_[i] = s;
        s->index_ = i;

        s->set_flags((sh_flags_e)swap(shdr[i].sh_flags));
        s->set_vaddr(swap(shdr[i].sh_addr));
        s->set_file_offset(offset);
        s->set_size(swap(shdr[i].sh_size));
        s->set_align(swap(shdr[i].sh_addralign));
        s->set_entsize(swap(shdr[i].sh_entsize));

        if (type != SHT_NOBITS && s->get_size())
          {
            fseek(file, offset, SEEK_SET);
            if (fread(s->get_content(), s->get_size(), 1, file) != 1)
              throw std::runtime_error("unable to read file");
          }

        obj.add_section(*s);
      }

    // update sections links

    for (unsigned int i = 1; i < shnum; i++)
      {
        section &s = *obj.secidx_[i];

        unsigned int link = swap(shdr[i].sh_link);

        if (link)
          s.set_link(obj.secidx_.at(link));

        unsigned int info = swap(shdr[i].sh_info);

        switch (s.type_)
          {
          case SHT_REL:
          case SHT_RELA:
            if (info)
              s.set_info(obj.secidx_.at(info));
            break;

          case SHT_DYNSYM:
          case SHT_SYMTAB:
            s.set_info_last(info);
            break;

          default:
            ;
          }
      }

    // set sections names

    unsigned int shstrndx = swap(head_.e_shstrndx);

    if (shstrndx != SHN_UNDEF)
      {
        section &shstr = *obj.secidx_.at(shstrndx);
        const char *str = (char*)shstr.get_content();

        for (unsigned int i = 1; i < shnum; i++)
          obj.secidx_[i]->set_name(str + swap(shdr[i].sh_name));

        delete &shstr;
      }

  }

  template <typename bits_t, int width>
  void elfn_access<bits_t, width>::create_segments(object &obj)
  {
     p_flags_e flag;

    
    FOREACH(sec, obj.get_section_table())
      {
        segment *s = new segment(obj);

        if(!(sec->get_flags() & elfpp::SHF_ALLOC))
        {
            s->set_type(PT_NULL);
            continue;
        }
        
        s->set_type(PT_LOAD);
        s->set_file_offset(0);//done while writing section in file
#ifdef MEMO_DEBUG
        std::cout << "seg building (" << std::hex << sec->get_vaddr() << ") for: " << *sec << std::endl;
#endif
        s->set_vaddr(sec->get_vaddr());
        s->set_paddr(sec->get_vaddr());

        s->set_mem_size(sec->get_size());
        s->set_file_size(sec->get_size());

            flag = PF_R ;//ALLOC ==> read ? 
            flag = flag | (p_flags_e)(sec->get_flags() & SHF_WRITE)? PF_W : PF_R ; 
            flag = flag | (p_flags_e)(sec->get_flags() & SHF_EXECINSTR)? PF_X : PF_R ; 
        s->set_flags(flag);
        s->set_align(0);//FIXME!

#ifdef MEMO_DEBUG
        std::cout <<"New segment " << s->get_file_size() << std::endl;
#endif
        obj.add_segment(*s);
      }
  }

  template <typename bits_t, int width>
  void elfn_access<bits_t, width>::write(object &obj, FILE *file)
  {
    byteorder_ = obj.byteorder_;

    if (obj.generate_symtab_)
      save_symtab(obj);

    // create all segments

    create_segments(obj);

    // write symbol contents

    FOREACH(sec, obj.get_section_table())
      {
        if (sec->get_type() == SHT_NOBITS)
          continue;

        FOREACH(sym_, sec->get_symbol_table())
          {
            symbol *sym = sym_->second;

            if (!sym->get_content())
              continue;

            if (sec->get_size() < sym->get_value() + sym->get_size())
              sec->set_size(sym->get_value() + sym->get_size());

            std::memcpy(sec->get_content() + sym->get_value(), sym->get_content(), sym->get_size());
          }
      }

    elf_hdr_t head;

    // create a new section name section

    section *shstrtab = new section(obj, SHT_STRTAB);
    shstrtab->set_name(".shstrtab");
    shstrtab->set_flags(SHF_STRINGS);
    obj.add_section(*shstrtab);

    size_t shnum = 1;

    FOREACH(s, obj.get_section_table())
      s->index_ = shnum++;

    std::string strtab(1, '\0');
    unsigned int stridx[shnum];

    stridx[0] = 0;

    FOREACH(s, obj.get_section_table())
      {
        stridx[s->index_] = strtab.size();
        strtab.append(s->get_name().c_str(), s->get_name().size() + 1);
      }

    shstrtab->set_size(strtab.size());
    std::memcpy(shstrtab->get_content(), strtab.data(), strtab.size());

    size_t phnum = shnum;//FIXME!:only relevent section
    // update header

    std::memset(head.e_ident, 0, sizeof(head.e_ident));
    std::memcpy(head.e_ident, ELFMAG, 4);
    head.e_ident[EI_CLASS] = obj.word_width_;
    head.e_ident[EI_DATA] = byteorder_;
    head.e_ident[EI_VERSION] = EV_CURRENT;
    head.e_ident[EI_OSABI] = obj.os_abi_;
    head.e_ident[EI_ABIVERSION] = obj.abi_ver_;

    swap(&head.e_type, obj.type_);
    swap(&head.e_machine, obj.machine_);
    swap(&head.e_version, EV_CURRENT);
    swap(&head.e_entry, obj.entry_);
    swap(&head.e_phoff, sizeof (elf_hdr_t));
    swap(&head.e_shoff, sizeof (elf_hdr_t)+ (sizeof(elf_phdr_t)*phnum));//!
    swap(&head.e_flags, obj.flags_);
    swap(&head.e_ehsize, sizeof (elf_hdr_t));
    swap(&head.e_phentsize, sizeof (elf_phdr_t));
    swap(&head.e_phnum, phnum);
    swap(&head.e_shentsize, sizeof (elf_shdr_t));
    swap(&head.e_shnum, shnum);
    swap(&head.e_shstrndx, shstrtab->index_);

    // update section table

    elf_shdr_t shdr[shnum];

    std::memset(shdr, 0, sizeof(shdr));

    FOREACH(s, obj.get_section_table())
      {
        unsigned int i = s->index_;

        swap(&shdr[i].sh_name, stridx[i]);

        swap(&shdr[i].sh_type, s->get_type());
        swap(&shdr[i].sh_flags, s->get_flags());
        swap(&shdr[i].sh_addr, s->get_vaddr());


        swap(&shdr[i].sh_size, s->get_size());
        if (s->get_link())
          swap(&shdr[i].sh_link, s->get_link()->index_);

        switch (s->get_type())
          {
          case SHT_REL:
          case SHT_RELA:
            assert(s->get_info());
            swap(&shdr[i].sh_info, s->get_info()->index_);
            break;

          case SHT_DYNSYM:
          case SHT_SYMTAB:
            swap(&shdr[i].sh_info, s->get_info_last());
          default:
            break;
          }

        swap(&shdr[i].sh_addralign, s->get_align());
        swap(&shdr[i].sh_entsize, s->get_entsize());
      }

    // update program header
    elf_phdr_t phdr[phnum];

    std::memset(phdr, 0, sizeof(phdr));

    unsigned int i = 1;//to keep the same order as sections
    FOREACH(s, obj.get_segment_table())
      {

        swap(&phdr[i].p_type, s->get_type());
        swap(&phdr[i].p_flags, s->get_flags());
        swap(&phdr[i].p_vaddr, s->get_vaddr());
        swap(&phdr[i].p_paddr, s->get_paddr());


        swap(&phdr[i].p_filesz, s->get_file_size());
        swap(&phdr[i].p_memsz, s->get_mem_size());

        
        swap(&phdr[i].p_align, s->get_align());
        //note: offset done while writing sections
        i++;
      }
    //assert((i == phnum)and (i == shnum));

    // write header to file

    fseek(file, 0, SEEK_SET);
    if (fwrite(&head, sizeof(head), 1, file) != 1)
      throw std::runtime_error("unable to write header to file");

    fseek(file, sizeof(phdr)+sizeof(shdr), SEEK_CUR);

    // write sections to file

    FOREACH(s, obj.get_section_table())
      {
        if (s->get_type() == SHT_NOBITS)
          continue;

#ifdef MEMO_DEBUG
        std::cout << "offset: " << ftell(file) << " for " << *s << std::endl;
        std::cout << std::hex << "paddr: " << phdr[s->index_].p_paddr << ", sect vaddr: " << s->get_vaddr() << "/" <<shdr[s->index_].sh_addr << std::endl;
#endif
        swap(&shdr[s->index_].sh_offset, ftell(file));
        swap(&phdr[s->index_].p_offset, ftell(file));
        if (s->get_size() && fwrite(s->get_content(), s->get_size(), 1, file) != 1)
          throw std::runtime_error("unable to write section to file");
      }
    
    // write program header to file

    fseek(file, sizeof(head), SEEK_SET);
    if (fwrite(phdr, sizeof(phdr), 1, file) != 1)
      throw std::runtime_error("unable to write section table to file");

    // write section table to file

    //toDO:assert(cur_seek == phnum*sizeof(ph_t)+...)
    //fseek(file, sizeof(phdr)+sizeof(head), SEEK_CUR);
    if (fwrite(shdr, sizeof(shdr), 1, file) != 1)
      throw std::runtime_error("unable to write section table to file");

  }

  template class elfn_access<elf32_bits_s, 32>;
  template class elfn_access<elf64_bits_s, 64>;

}